I've searched set-up and luthier, and not found a relevant thread, so please redirect me if I have missed something. My RBX765 is strung with lightweight Rotosound 66 stainless steel 125/100/80/60/40g strings, tuned BEADG. The problem that I have is a 'cheap car stereo' boom about the F on the B string or the C on the E string. It is less obvious with new strings, and gets worst from there. It is not a fret buzz, or a room/speaker resonance. It does not appear to be an electronics problem, because the same notes on other strings sound much better, and it does not appear to be a pick-up problem, because the better sounding F is on the E string. Is this a dead-spot type problem with this bass, or a string incompatibility problem, or some other resonance that you can tell me how to track down?